The present invention relates to fluorinated crosslinked polymers modified with hydrogenated monomers, the processes for obtaining them and the manufactured articles therefrom.
In particular the invention relates to curable compositions, comprising thermoprocessable copolymers of ethylene (E) with tetrafluoroethylene (TFE) and/or chlorotrifluoroethylene (CTFE) modified with acrylic monomers, subjected to ionizing radiations comprising X rays, gamma rays, electron beams and the like. The preferred sources of ionizing radiation include Cobalt-60, which emits high penentration gamma radiations and high energy electron beams.
It is well known in the art the crosslinking of the thermoprocessable ETFE and ECTFE copolymers by ionizing radiations (U.S. Pat. No. 3,738,923) also in the presence of crosslinking agents well known in the prior art such as triallylisocyanurate (TAIC), triallylcyanurate (TAC) and others, as reported in U.S. Pat. No. 3,763,222, U.S. Pat. No. 3,840,619, U.S. Pat. No. 4,039,631 and U.S. Pat. No. 4,121,001.
Unfortunately, to obtain a meaningful improvement of the mechanical properties higher doses of ionizing radiation are required. For example in the case of xcex3 radiation, higher than 10 megarad (MRad), must be used. It is well known that high levels of irradiation can be obtained by using high intensity irradiation systems which are complex for safety reasons, or by irradiating with a low intensity irradiation system for longer times. Both cases are economically disadvantageous. Furthermore and most important, a high dose of radiation implies the strong risk to decompose the starting polymer with possible formation of gaseous products.
It would be therefore desirable to operate at the lowest possible level of radiation intensity obtaining a crosslinked product having improved mechanical properties.
It is known the use of the ETFE and ECTFE thermoprocessable polymers as materials for the electric insulation as wire insulation and jacketing cables. Besides, it is also known that the crosslinking improves the mechanical properties of the fluoropolymers at high temperatures.
In view of the above, it was desirable to increase the thermal rating of the fluoropolymers used as wire insulation or as jacketing cable, by improving their mechanical properties at high temperatures, in particular increasing the stress at break without jeopardizing the elongation at break.
The Applicant has surprisingly and unexpectedly found a crosslinked polymer composition of thermoprocessable copolymers of ethylene (E) with tetrafluoroethylene (TFE) and/or chlorotrifluoroethylene (CTFE) modified with acrylic monomers and a crosslinking agent, which subjected to ionizing radition, are capable to crosslink at very low radiation levels, at which the ETFE and ECTFE copolymers do not crosslink, without decomposition of the thermoprocessable copolymer achieving improved mechanical properties at high temperatures. In particular the increase of the stress at break without jeopardizing the elongation at break which remains higher than 100%, conditions which are required in wire insulation and jacketing cable applications.
Therefore, an object of the present invention are crosslinked polymer compositions obtainable by subjecting to ionizing radiations compositions comprising:
I) thermoprocessable copolymers of ethylene with tetrafluoroethylene (TFE) and/or chlorotrifluoroethylene (CTFE) modified with acrylic monomers of formula:
CH2xe2x95x90CHxe2x80x94COxe2x80x94Oxe2x80x94R2xe2x80x83xe2x80x83(a)
R2 is a hydrogenated radical from 1 to 20 carbon atoms, C1-C20, alkyl, linear and/or branched radical, or cycloalkyl, or R2 is H. The radical R2 can optionally contain: heteroatoms preferably Cl, O, N; one or more functional groups preferably selected from OH, COOH, epoxide, ester and ether; and double bonds;
II) one or more cross-linking agents;
III) one or more optional ingredients.
The thermoprocessable copolymers of component I) comprise from 10 to 70%, preferably from 35 to 55%, by moles of ethylene, from 30 to 90%, preferably from 45 to 65%, by moles of a fluorinated monomer selected from tetrafluoroethylene, chlorotrifluoroethylene, or mixtures thereof, from 0.1 to 30%, preferably from 1 to 15% by moles of the comonomer (a).
The preferred fluorinated monomer of component I) is chlorotrifluoroethylene.
n-Butylacrylate (n-BuA) is the preferred acrylic monomer.
The cross-linking agents of component II) can be for example triallylisocyanurate (TAIC), triallylcyanurate (TAC), diallylisophthalate (U.S. Pat. No. 4,039,631), diallylterephthalate (U.S. Pat. No. 4,039,631), esters of phenyl indan (U.S. Pat. No. 3,763,222), triallylester of the aryl polycarboxylic acid (U.S. Pat. No. 3,840,619), bisolefins such as for example 1,6 divinylperfluorohexane (see U.S. Pat. No. 5,612,419) and others (see U.S. Pat. No. 4,121,001).
The preferred crosslinking agent is triallylisocyanurate.
The cross-linking agent amounts ranges from 0.1 to 10.0% by weight, preferably from 0.3 to 5.0% by weight, more preferably from 0.5 to 2.0% by weight referred to the crosslinkable composition.
The components III) can be fillers (for example polytetrafluoroethylene (PTFE), silicates), smoke retarders, lubricants, pigments, fire retardants, intumescent agents, plasticizers (for example MORFLEX(copyright) 560), metal oxides (ZnO, MgO), thermal stabilizers such as for example Irganox(copyright) 1010. The maximum total amount of said optional ingredients is 30.0% by weight referred to the crosslinkable composition.
A further object of the present invention is a crosslinking process by ionizing radiations of the crosslinkable polymer compositions of the invention.
The ionizing radiations used for the crosslinking can be X rays, xcex3 rays, electron beams, deuterons, xcex1 particles or their combinations. The radiation amounts can range from 0.1 to 10 Mrad, preferably from 0.2 to 5 Mrad, more preferably from 0.5 to 2 Mrad.
Another object of the present invention are manufactured articles of the crosslinked polymer compositions of the invention, in particular cables.
Furthermore it is possible to obtain multilayer manufactured articles by irradiating the multilayer article of crosslinkable polymer compositions of the present invention and hydrogenated polymers. Applications of particular interest are, in the car industry, the preparation of fuel lines and fuel hoses which are multilayer manufactured articles of hydrogenated and fluorinated polymers. For fuel lines is meant essentially a bilayer system of thermoplastic hydrogenated polymers and crosslinkable polymer compositions of the present invention, and then irradiated as above mentioned. For fuel hoses is meant essentially a bilayer system of hydrogenated elastomers and crosslinkable polymer compositions of the present invention, and then irradiated as above mentioned. Therefore, a further object of the present invention are multilayer articles of crosslinked polymer compositions of the present invention and hydrogenated polymers.
As examples of hydrogenated polymers we can mention thermoplastic polymers, and hydrogenated elastomers.
as thermoplastic polymers: for example cellulose polymers, polyamides such as NYLON 6, NYLON 66, NYLON 11, NYLON 12, polyamide copolymers, polycarbonates, polyesters, such as polyethylenterephthalate, polyester copolymers, polyolefins such as high and low density polyethylene, olefine copolymers, polyimides, polystyrene, polyurethanes, polyvinylchloride (PVC), polysulphones, ethylene/vinylacetate copolymers, polyacrylbutadienestyrene (ABS);
as elastomeric hydrogenated polymers: for example acrylic rubbers, nitrile rubbers (NBR), ethylene-propylene rubbers (EPM), ethylene-propylene-diene rubbers (EPDM), NVC rubbers (nitrile NBR rubbers mixed with PVC), epichlorohydrin rubbers (CO and ECO).
In particular for fuel lines applications polyamides are preferred. For fuel hoses applications epichlorohydrin and nitrile rubbers (NBR) are preferred.
For the preparation of fuel lines the coextrusion of polyamides and of the components I), II) and III), and then irradiating with ionizing radiations is preferred. For the preparation of the fuel hoses the extrusion of the hydrogenated rubber on a tube formed of components I), II) and III), and then irradiating with ionizing radiations is preferred.